…but it’s also very centralized. I had harder to find any good figures for cloud hosts. Sorry for the raw links.
Use of Twitter: http://www.idg.se/2.1085/1.375038/140-miljoner-meddelanden-senare—twitter-fyller-5-ar
As in 140 million messages per day! Even though we are talking short text snippets (all else is handled by companies outside of Twitter), they need a few servers for this, but a far cry from Facebook, as it handles much more complex and spacious data..
GroupOn’s revenue: http://www.businessinsider.com/groupon-revenue-run-rate-2010-12
Facebook’s revenue: http://mashable.com/2011/01/17/facebooks-ad-revenue-hit-1-86b-for-2010/
“All told, Williamson said Facebook alone accounted for 5% of all online ad spend in 2010; she expects that number to rise to 8% in 2011.”
In other words a market worth 40B now and much more in the future, increasingly with ads viewed via mobile devices. I wonder why Facebook’s app doesn’t show ads yet. It no doubt will in the near future.
Facebook’s servers (note: June 2010, so more now): http://www.datacenterknowledge.com/archives/2010/06/28/facebook-server-count-60000-or-more/
Twitter’s revenue (not so much yet):
Foursquare’s revenue (not so much either): http://techcrunch.com/2010/02/12/foursquare-revenue/